Golf club shaft having wave shaped reinforced part

ABSTRACT

The present invention relates to a golf club shaft having improved torsion characteristics comprising a base shaft having an internal surface and an external surface, and at least one wave shaped reinforced part on at least one of said surfaces, said wave shaped reinforced part comprising a plurality of reinforcement pieces. The wave shaped reinforced part is located on at least one of the upper portion, midpoint or lower portion. The golf club shafts of the present invention can be made by applying a base section of a prepreg sheet or assembly having a plurality of finger like elements to a portion of a base shaft, wrapping the finger like elements around the base shaft to provide a wave shaped reinforced part having a plurality of reinforcement pieces, and curing the shaft having the wave shaped reinforced part thereon to produce a golf club shaft having a wave shaped reinforced part. Golf clubs made with the shafts of the present invention impart greater flying distance and/or directional accuracy to golf balls struck by the golf clubs. The wave shaped reinforced part provides a means of moving the kick point of the shaft to achieve a desired effect on flying distance and/or accuracy. The present invention provides a convenient means of adjusting the characteristics of a golf club shaft according to the skill level of the intended user.

[0001] This application is a continuation of Ser. No. 10 042 541 filedon Oct. 19, 2001 which is a continuation of Ser. No. 09/472,219 filed onOct. 26, 1999, now abandoned which is a continuation of Ser. No.08/896,722 filed on Jul. 18, 1997, now abandoned which was acontinuation-in-part of Ser. No. 29/061,700 filed on Oct. 29, 1996, nowU.S. Pat. No. D 401,981 and Ser. No. 08/760,079 filed on Dec. 4, 1996,now abandoned. This application claims the benefit of U.S. ProvisionalApplication No. 60/047,697 filed on May 23, 1997.

BACKGROUND OF THE INVENTION

[0002] Since a carbon (graphite) shaft is lighter than a conventionalsteel shaft, the head speed of a golf club while swinging is increased,thus increasing the flying distance of a ball struck by the golf club.However, a graphite shaft has a disadvantage in that its torsioncharacteristics are poor. If the torsion characteristics of the shaftare poor, the sweet spot of the club head typically does not strike theball during impact. When the ball is impacted by areas of the club headother than the sweet spot, the direction of the ball in flight is notexact.

[0003] According to conventional methods for improving torsioncharacteristics of a shaft, first, the fiber orientation (angle formedby the axis of the shaft with the textile tissue of carbon fiber withinprepreg sheet) of torsion layer should be ±45° and the prepreg sheetsare used for rolling the shaft several times; however, this method hasdisadvantages in that flex strength is significantly reduced and theweight of the shaft is increased, even though torsion characteristicsare improved.

[0004] Second, steel or aluminum alloy is installed internally and ontop of it, prepreg sheets are laminated in such a manner that thetextile tissue of carbon fiber (mesh) is at the same position as theaxial direction of the shaft; however, the use of steel-type internalconduit may be responsible for increasing weight, thus adverselyaffecting the light weight of a carbon shaft.

[0005] Meantime, for the improvement of flying distance of a golf ball,much research has focused on the enhancement of golf club head shape andmaterial instead of the golf club shaft. However, the shaft is one ofthe important factors which influences the flying distance of a golfball. The relevant conventional methods are as follows:

[0006] Korean Patent Open-Laid No. 95-23427 describes a method ofproviding some reinforced lines within the shaft but this method hassome disadvantages in that the weight of shaft increases.

[0007] Korean Patent Open-Laid No. 96-1936 describes a method of formingthe hollow part within the shaft with a hexagon or octagon but itsmanufacturing process is very complicated over the enhanced effects offlying distance.

[0008] Although these methods of the prior art provide shafts which maybe used in golf clubs, these shafts suffer from the disadvantagesdescribed above. A need therefore exists for golf club shafts and golfclubs which overcome disadvantages such as those described above.

SUMMARY OF THE INVENTION

[0009] The present invention relates to a golf club shaft comprising abase shaft having an internal surface and an external surface, and atleast one wave shaped reinforced part on at least one of the surfaceswherein the wave shaped reinforced part has a plurality of reinforcementpieces. The wave shaped reinforced part is located on at least one ofthe upper portion, midpoint or lower portion.

[0010] The golf club shafts of the present invention can be made byapplying a base section of a prepreg sheet or assembly having aplurality of finger like elements to a portion of a base shaft, wrappingthe finger like elements around the base shaft to provide a wave shapedreinforced part having a plurality of reinforcement pieces, and curingthe shaft having the wave shaped reinforced part thereon to produce agolf club shaft having a wave shaped reinforced part thereon.

[0011] Golf clubs made with the golf club shafts having at least onewave shaped reinforced part impart greater flying distance and/ordirectional accuracy to golf balls struck with the golf clubs. The waveshaped reinforced part improves the torsion characteristics of the golfclub shaft and provides a means of changing the location of the kickpoint of the shaft to achieve a desired effect on flying distance and/ordirectional accuracy. The present invention provides a convenient meansof adjusting the characteristics of a golf club shaft according to theskill level of the intended user.

[0012] Having summarized the invention, the invention will now bedescribed in detail by reference to the drawings, detailed descriptionand non-limiting examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a front view of a golf club shaft in accordance with afirst embodiment of the invention in which a wave-shaped reinforced partis provided at the lower part of the shaft.

[0014]FIG. 2 is a front view of a golf club shaft in accordance with asecond embodiment of the invention in which a wave-shaped reinforcedpart is provided at the upper part of the shaft below the grip end.

[0015]FIG. 3 is a front view of a golf club shaft in accordance with athird embodiment of the invention in which wave-shaped reinforced partsare provided at both the lower part and the upper part of the shaft.

[0016]FIG. 4 is a front view of a golf club shaft in accordance with afourth embodiment of the present invention in which a wave-shapedreinforced part is provided at the middle part of the shaft.

[0017]FIG. 5 is a front view of a golf club shaft in accordance with afifth embodiment of the present invention in which a wave-shapedreinforced part is provided at a location midway between the grip end ofthe shaft and the middle point of the shaft.

[0018]FIG. 6 is a partial longitudinal sectional view of a portion ofthe shaft according to the invention having a wave shaped reinforcementpart that has a sinusoidal configuration.

[0019]FIG. 7 shows frontal views of other possible shapes of waves ofwave shaped reinforcement parts useful in the invention.

[0020]FIG. 8 shows the preparatory state of forming the wave shapedreinforced part before wrapping finger like elements of the prepregsheet around the shaft. The base section of the prepreg sheet orassembly is attached to the base shaft and the finger like elements areshown in an extended state.

[0021]FIG. 9 is a perspective view of a section of a reinforced part ofa golf club shaft according to the invention prior to curing of a waveshaped reinforced part showing some of the finger like elements of aprepreg sheet wound around the base shaft to form reinforcement pieces.FIG. 9 also shows some of the finger like elements in an extended stateprior to winding around the base shaft.

[0022]FIG. 10 shows shaped reinforcement pieces that are formed bywrapping the finger like elements of the prepreg sheet around the shaft.One of the finger like elements is shown in an extended state toillustrate the effect of forming the finger like elements. The figurealso shows a view of tape that is wrapped around the reinforcementpieces prior to curing.

[0023]FIG. 11 shows a golf club shaft having a wave shaped reinforcementpart that partially encircles a base shaft.

[0024]FIG. 12 shows a golf club shaft that has rib shaped reinforcementpieces.

[0025]FIG. 13 shows a golf club shaft having a wave shaped reinforcementpiece on the interior of the shaft.

[0026]FIG. 14 is a frontal view of a golf club made with a firstembodiment of a golf club shaft of the invention in which a wave-shapedreinforced part is provided at the lower part of the base shaft abovethe hosel.

[0027]FIG. 15 is a frontal view of a golf club made with a secondembodiment of a golf club shaft of the invention in which a wave-shapedreinforced part is provided at the upper part of the shaft below thegrip

[0028]FIG. 16 is a frontal view of a golf club made with a thirdembodiment of a golf club shaft of the invention in which wave-shapedreinforced parts are provided at both the lower part and the upper partof the shaft.

[0029]FIG. 17 shows a golf club made with a fourth embodiment of a golfclub shaft of the invention in which a wave-shaped reinforced part islocated at the midpoint of a base shaft.

[0030]FIG. 18 shows a golf club made with a fifth embodiment of a golfclub shaft of the invention in which a wave-shaped reinforced part islocated between the midpoint and the grip end of the shaft.

DETAILED DESCRIPTION OF THE INVENTION

[0031]FIG. 1 shows a first embodiment of the golf club shaft 25A of thepresent invention, in which a wave shaped reinforced part 1 is formed inthe lower portion of the golf club shaft. The lower portion of the shaftthat portion between the midpoint of the entire length of the shaft andthe upper edge 12 of the hosel section. FIG. 1 shows the preferredlocation a of the reinforced part near hosel section 15. The wave shapedpart 1, however, may be located at other positions between the upperedge of the hosel section and the midpoint of the lower portion of theshaft. When wave shaped reinforced part 1 is provided at location a ofbase shaft 5, there is a significant improvement in torsioncharacteristics of the golf club shaft.

[0032] The wave shaped reinforced parts of the golf club shafts of thepresent invention are made up of reinforcement pieces. In wave shapedreinforced part 1, the number of reinforcement pieces is 1 to 6reinforcement pieces, more preferably 1 to 3 reinforcement pieces.Although a larger number of reinforcement pieces may be applied to theshaft, it is preferred to use at most 6 pieces to minimize thepossibility that the weight of the golf club shaft may become excessiveand thus reduce the flying distance of the ball.

[0033] Typically, when the number of reinforcement pieces in wave shapedreinforced part 1 is 3 pieces, about 10 percent improvement in torsioncharacteristics may be expected. As a result, even though the ball isnot hit by the sweet spot of the golf club head during impact, the ballgenerally goes in the desired direction and a bad hook or slice isprevented. Also, when wave-shaped reinforced part 1 is provided at thelower part a of base shaft 5, the kick point moves upward.

[0034] The length of wave shaped reinforced part 1 is about 2 cm toabout 15 cm, preferably about 3 cm to about 10 cm.

[0035]FIG. 2 shows a second embodiment of the invention in which a waveshaped reinforced part 1′ is provided in the upper portion of the golfclub shaft. The upper portion of the golf club shaft is that portionbetween the midpoint of the entire length of the shaft and the loweredge of the grip section of the shaft. FIG. 2 shows the preferredlocation b of the wave shaped reinforced part near grip section 22.However, the wave shaped reinforced part 1′ may be located at otherpositions between the midpoint of the upper portion of shaft and thelower edge of the grip section. When wave-shaped reinforced part 1′ isprovided at location b, the kick point of golf club shaft 25B movesdown, away from the grip end 20.

[0036] The total length of wave shaped reinforced part 1′ can range fromabout 2 cm to about 20 cm, preferably about 3 cm to 15 cm. In waveshaped reinforced part 1′, the number of reinforcement pieces is 1 to 7reinforcement pieces, more preferably 3 to 5 reinforcement pieces.Although a larger number of reinforcement pieces may be applied to theshaft, it is preferred to use no more than 7 pieces to minimize thepossibility that the weight of the golf club shaft may become excessiveand thus reduce the flying distance of the ball.

[0037] Generally, if the kick point is located closer to the grip end ofthe shaft, the flying distance of the ball is enhanced but the directionof the ball is less accurate. In addition, it may become very difficultto make a swing that will produce exact impact at the point where theforce of shaft is maximized, creating much difficulty for amateurgolfers.

[0038] However, since golf club shafts such as the shaft illustrated inFIG. 2, cause the kick point to move down, the golf club shafts of theinvention overcome the aforementioned shortcomings so as to make anexact swing and impact much easier even for amateur golfers. Inaddition, any loss of flying distance produced by the move-down of thekick point can be countered by extending the length of the base shaft 5.The length of base shaft 5 therefore can be increased to cause the kickpoint of the resulting golf club shaft to have the same height (from tip10 of the shaft) as the original height of the kick point on base shaft5 prior to forming the wave shaped reinforced part thereon so that theflying distance of the ball increases.

[0039] Without wishing to be bound by theory, the following Table 1shows typical percentages of movement of the kick point which may beexpected depending on the number of reinforcement pieces in a waveshaped reinforced part when applied to location b of a base shaft. TABLE1 PERCENTAGE OF MOVEMENT OF THE KICK NUMBER OF POINT (the percentdecrease in the height of the REINFORCEMENT kick point measured from theclub head tip of the PIECES shaft) 3 3% 5 5% 7 7%

[0040] Thus, if the height of the kick point of a base shaft (measuredfrom the club head tip 10) is 15 cm without a wave shaped reinforcedpart 1′, then forming a wave shaped reinforced part having 3reinforcement pieces at the upper part b of the base shaft moves thekick point “down” to a height 14.5 cm (measured from club head tip 10).This is a 3% decrease in height from the original height of the kickpoint of the base shaft.

[0041]FIG. 3 shows a third embodiment of the invention in which waveshaped reinforced parts 1 and 1′ are located at both the lower and upperportions of the golf club shaft. FIG. 3 shows the wave shaped reinforcedpart at the preferred location a near hosel section 15 and the preferredlocation b near grip section 22 respectively of base shaft 5. However,part 1 may be located at other positions between the midpoint of thelower portion of the shaft and the upper edge of the hosel section 15.Likewise, part 1′ may be located at other positions between the midpointof the upper portion of the shaft and the lower edge of the gripsection. When reinforced parts 1 and 1′ are provided at both location aand location b of the base shaft 5, improvement of ball flight directionmay be expected together with a more convenient and exact swing.

[0042] In this embodiment, the total number of reinforcement pieces inwave shaped reinforced parts 1 and 1′ is 5 to 7 pieces. The wave shapedreinforced part 1′ located at upper part b preferably has a largernumber of reinforcement pieces than wave shaped reinforced part 1located at lower part a. Reinforced part 1 typically has 2 to 3 piecesand a length of about 2 cm to about 8 cm. Wave shaped reinforced part 1′typically has 4 to 5 pieces and a length of about 10 cm to about 15 cm.

[0043] When wave shaped reinforced parts 1 and 1′ are provided asdescribed in this embodiment, improvement of ball flight direction alsomay be expected together with a more convenient and exact swing. Also,the direction of the kick point moves down relative to the kick point ofthe base shaft.

[0044]FIG. 4 shows a fourth embodiment of the present invention, inwhich a wave shaped reinforced part 1A is provided at midpoint m of thelength of the base shaft 5. If the wave shaped reinforced part 1A isprovided at midpoint m, the kick point moves down relative to thelocation of the kick point of the base shaft 5.

[0045] In this embodiment, reinforced part 1A typically has 5 to 7pieces and a length of 2 cm to about 20 cm, preferably about 3 cm toabout 15 cm. When reinforced part 1A is provided at midpoint m of baseshaft 5, improvement of ball flight direction also may be expectedtogether with a more convenient and exact swing.

[0046] The position of wave shaped reinforced part 1A relative tomidpoint m may vary. For example, wave shaped reinforcement part 1A maybe provided so as to cause wave shaped reinforced part 1A to extendequally on each side of midpoint m. Wave shaped reinforced part 1A alsocan be positioned to have unequal portions thereof extend on either sideof midpoint m.

[0047]FIG. 5 shows a fifth embodiment of the present invention in whicha wave shaped reinforced part 1B is provided midway between the loweredge of grip section 22 and midpoint m of the base shaft 5. In the golfclub shaft shown in FIG. 5, the kick point moves down relative to thelocation of the kick point of the original base shaft 5. In thisembodiment, reinforced part 1B typically has 5 to 7 pieces and a lengthof about 10 cm to about 20 cm. When reinforced part 1B is provided atmidpoint m of base shaft 5, improvement of ball flight direction alsomay be expected together with a more convenient and exact swing.

[0048]FIG. 6 is a partial cross sectional view of a portion of the shaftaccording to the invention having a wave shaped reinforced part that hasa sinusoidal configuration, i.e., the surfaces of the waves are curvedas opposed to an angular or compressed wave configuration. Thereinforcement pieces of the wave-shaped reinforced parts of the golfclub shafts of the invention preferably have a sinusoidal configurationas shown, for example, in FIG. 6.

[0049] The shape of the waves formed by reinforcement pieces may havealternative configurations such as, for example, square waveconfiguration, triangular wave configuration, compressed waveconfiguration, and trapezoidal configuration. Examples of thesealternative configurations are shown in FIG. 7 which shows frontal viewsof other possible configurations of wave shaped reinforced parts used inthe invention.

[0050] Base Shaft

[0051] The base shafts that can be employed to make the golf club shaftsof the present invention include, but are not limited to, commerciallyavailable graphite shafts, titanium shafts, steel shafts, fiberglassshafts and other shafts that are suitable for use in making golf clubs.Graphite shafts are preferred as the base shaft. The base shaft can bein an unfinished state, i.e., prior to application of finishingmaterials such as lacquers. Finished shafts that have been treated withfinishing materials can also be used as the base shaft.

[0052] Many prior art golf club shafts such those disclosed in KoreanPatent Application No. 96-1939 require complicated manufacturingprocesses. An advantage of the present invention over golf club shaftsof the prior art is that commercially available base shafts can be usedto produce the golf club shafts according to the invention. The presentinvention provides a convenient means of moving the kick point of thegolf club shafts according to the skill level of the intended user.

[0053] Prepreg Sheet Starting Material

[0054] Prepreg is the composite industry's term for continuous fiberreinforcement material which is pre-impregnated with a partially curedpolymer resin. Prepreg sheets are well known in the art Prepreg sheetsare produced by known methods such as that disclosed in Callister,William D., Materials Science and Engineering: An Introduction, JohnWiley & Sons, Inc, N.Y. (1994) herein incorporated by reference.Commercially available prepreg sheets can be used to form wave shapedreinforced parts of the golf club shaft according to the invention.

[0055] Prepreg sheets useful in the invention include carbon fiberreinforced prepreg sheets wherein the carbon fibers run in a singledirection. Glass fiber reinforced prepreg sheets can also be usedwherein the glass fibers are woven to intersect each other in aperpendicular orientation forming a criss-cross pattern. In a preferredembodiment of the invention, the prepreg sheet starting material is anassembly of a glass fiber prepreg sheet on top of a carbon prepreg sheetso that the glass prepreg sheet is on the outside surface of thereinforced part. This type of assembly prevents the carbon fibers fromleaking or peeling off during the manufacturing process.

[0056] Prepreg sheets useful in the invention include but are notlimited to those which are impregnated with a thermoplastic resin,preferably epoxy resin. The thickness of the prepreg sheet is typicallybetween about 0.1 mm to about 0.15 mm. An example of a carbon fiberprepreg sheet useful in the invention is known as T700 and was obtainedthrough Korea Fiber Co. of Korea.

[0057] Total Weight of Golf Club Shaft with Reinforced Part(s)

[0058] The desired total weight of the golf club shaft with wave shapedreinforced part(s) is an important factor in determining the appropriatethickness of the prepreg sheet and the thickness of the reinforcementpieces. Typical total weights of the golf club shaft can range fromabout 70 g to about 100 g. It is preferred that the total weight of agolf club shaft for a driver in accordance with the invention which hasthree or more wave shaped reinforced parts is about 70 g to about 75 g.The preferred total weight for a golf club shaft of the invention whichhas three or more wave shaped reinforced parts, when used in a 5-iron,is about 68 g to about 72 g.

[0059] Prepreg Sheet Base Section and Finger Like Elements

[0060]FIG. 8 shows base section 2B of prepreg sheet 2A attachedvertically onto a portion of base shaft 5. As illustrated in FIG. 8,prepreg sheet 2A has finger like elements 2 that are formed by removingsections from a prepreg sheet starting material. The base section 2B ofprepreg sheet 2A is attached to base shaft 5, and finger like elements 2are shown in a position for wrapping around and onto base shaft 5.Generally, the length of base section 2B of a prepreg sheet correspondsto the desired length of the wave shaped reinforced part.

[0061] As discussed in more detail below, prepreg sheet 2A can be madefrom a single prepreg sheet or an assembly of prepreg sheets such as aglass fiber prepreg sheet on top of a carbon fiber prepreg sheet. Theassembly is cut to form a prepreg sheet 2A with finger like elements 2.

[0062] The finger like elements 2 preferably have an elongated, taperedshape as shown in FIG. 8. Although it is preferred to use finger likeelements 2 which have a tapered shape, finger like elements 2 may have avariety of shapes depending on the configuration of the waves desired inthe wave shaped reinforced part. The shape of the finger like elements 2may be readily determined by those of ordinary skill in the artdepending on the configuration of the waves desired in the wave shapedreinforced part.

[0063] Finger like elements 2 are formed by cutting a prepreg sheet orassembly by known means such as utility knives, carbide disk cutters,and the like. More advanced cutting means includes die cutting and lasercutting. In the example shown in FIG. 8, finger like elements 2 arecurved toward the grip end of the base shaft 5. This configuration isuseful to form reinforcement pieces which yield a wave shaped reinforcedpart that has a sinusoidal configuration. The degree of curvature of thefinger like elements used to form a wave shaped reinforced part that hasa sinusoidal configuration can readily be determined according to thesize and shape of a particular base shaft. For example, when the baseshaft tapers in the direction of the club head tip of the base shaft,the length of finger like elements 2 can be increased as the radius ofthe base shaft decreases toward the tip end of the shaft.

[0064] Shape of the Reinforcement Pieces

[0065] The outer shape of the reinforcement pieces which form awave-shaped reinforced part can be formed according to the type of wavedesired in the wave shaped reinforced part. For example, thereinforcement pieces may have a sinusoidal shape to provide a waveshaped reinforced part having a sinusoidal configuration as shown inFIG. 6. Similarly, the reinforcement piece may have other shapes toprovide wave shaped reinforced parts which have, for example, compressedwave configurations, triangular wave configurations, square waveconfigurations and the like as shown in FIG. 7. Other possibleconfigurations include arc, tetragonal or spiral configurations. Aparticular configuration can be formed by sanding the waves to thedesired configuration. A wave shaped reinforced part that has a spiralform can be formed, for example, by forming a “rope” from carbon fibers.The “rope” is wound spirally around a base shaft to form the desirednumber of reinforcement pieces.

[0066] Thickness of the Reinforcement Pieces

[0067]FIG. 9 shows a section of a golf club shaft having a wave shapedreinforced part prior to curing. FIG. 9 also shows finger like elements2 extended prior to winding around the shaft. During manufacture, fingerlike elements 2 are wrapped around base shaft 5 to form reinforcementpieces 30 having thickness T and overall diameter D. The thickness T ofreinforcement pieces such as those shown in FIG. 9 is a function of 1)the desired total weight of the golf club shaft with the wave shapedreinforced part and 2) the taper of the shaft. The thickness T of thereinforcement pieces is at least about 0.5 mm. Typically, the maximumthickness of the reinforcement pieces is about 1.5 mm to maintain thetotal weight of the golf club shaft within current commerciallydesirable weight limits.

[0068] In one embodiment of the golf club shaft of the invention, theoverall diameters D as shown in FIG. 9 of the base shaft andreinforcement pieces in a wave shaped reinforced part are the same. Inthis embodiment, the thickness T of each reinforcement piece can varydepending on the taper of the shaft. For example, as the diameter of thebase shaft decreases, the thickness T of reinforcement pieces canincrease so that the overall diameters D of the base shaft andreinforcement pieces is constant. In another embodiment, the thicknessesof the reinforcement pieces is constant and the overall diameters D ofthe base shaft and the reinforcement pieces can vary.

[0069] Manufacture and Assembly

[0070] A golf club shaft of the invention is formed by bonding a prepregsheet or, preferably, a prepreg sheet assembly onto a base shaft. Theprepreg sheet or assembly includes a base section and finger-likemembers joined to the base section. The finger-like members are wrappedaround the base shaft to provide a wave shaped reinforced part.

[0071] In one embodiment of the manufacture of the golf club shafts ofthe invention, the base section of a prepreg sheet or assembly havingfinger like elements 2 as shown, for example, in FIG. 8, is attachedvertically along the length of a desired section of a base shaft by anadhesive such as epoxy resin. Finger like elements 2 are wrapped aroundbase shaft 5 to produce reinforcement pieces 30 such as those shown, forexample, in FIG. 9.

[0072]FIG. 10 shows a section of a golf club shaft having a wave shapedreinforced part wherein the reinforcement pieces are covered by tape 40prior to curing. FIG. 10 also shows a finger like element 2 extendedprior to winding around the shaft. During manufacture, finger likeelements 2 are wrapped around base shaft to form reinforcement pieces 30having thickness T and overall diameter D. The resulting wave shapedreinforced part can be covered with carbon tape 40 prior to curing asshown in FIG. 10. The wave shaped reinforced part is cured by heat at anappropriate temperature for the particular prepreg sheet. Generally, thecuring temperature and time are functions of the particular prepregsheet starting material. Curing temperatures and times are widely knownand published for various prepreg sheets that can be used alone or in anassembly in the present invention. One skilled in the art can readilydetermine the time and temperature values for the specific prepreg sheetbeing used, the length of the reinforced part, and the number andthickness of the reinforcement pieces. The time and temperatures can beselected for full or limited cure.

[0073] Although it is preferred to bond a prepreg sheet or assemblyaround a base shaft as described above, a wave shaped reinforced parthaving a sinusoidal configuration shown in FIG. 6 or any of the otherconfigurations shown in FIG. 7 may be formed by well known techniquessuch as compression molding, flame spraying, plasma deposition and thelike.

[0074] In a first embodiment of a compression molding method useful inthe invention, one or more layers of uncut prepreg sheet material iswrapped onto the surface of the shaft. The wrapped shaft then iscompressed under heat and pressure in a mold having the desiredconfiguration of the waves in the wave shaped reinforced part.Preferably, the wave shaped reinforced part such as reinforced part 1,1′ is formed on the exterior surface of base shaft 5.

[0075] As an alternative to compression molding, techniques such asflame spraying may be employed to deposit material onto the surface ofthe shaft to yield a wave shaped reinforced part having a desired waveshape on selected portions of the base shaft.

[0076] Although it is preferred that the wave shaped reinforced partcompletely encircle the base shaft as shown, for example, in FIG. 10, awave shaped reinforced part 32 may be formed on selected portions ofshaft 25I which only partially encircles the shaft as shown in FIG. 11.Wave shaped reinforced parts which only partially encircle the shaft mayreadily be formed by techniques such as compression molding and flamespraying. Techniques such as compression molding and flame spraying areespecially suitable for forming a golf club shaft 25F which has, forexample, rib shaped reinforcement pieces 31 as shown in FIG. 12.

[0077] Compression molding also may be used for example, to form a waveshaped reinforcement pieces 30 on the internal surface of a base shaft25G as shown for example, in FIG. 13. In this aspect, a rod havingexpandible sections may be inserted into a base shaft. The expandiblesections of the rod then are compressed against the interior surface ofthe base shaft to form reinforcement pieces. Preferably, thereinforcement pieces are wave shaped to produce a wave shaped reinforcedpart that has a sinusoidal configuration. Other wave shapes, e.g., anyof those shown in FIG. 7, may be made by compression molding.

[0078]FIG. 14 shows a golf club made from a first embodiment of golfclub shaft 25A of the present invention in which a wave shapedreinforced part 1 is located at the lower part a of a base shaft 5 nearhosel section 15. When wave shaped reinforced part 1 is provided at thelower part a of base shaft 5, there is a significant improvement intorsion characteristics of the golf club shaft.

[0079]FIG. 15 shows a golf club made from a golf club shaft 25B inaccordance with a second embodiment of the invention in which waveshaped reinforced part 1′ is located at location b of the golf clubshaft near the grip 27. When wave-shaped reinforced part 1′ is providedat location b, the kick point of golf club shaft 25B moves down, awayfrom the grip 27.

[0080]FIG. 16 shows a golf club made from a golf club shaft 25C inaccordance with a third embodiment of the invention in which wave shapedreinforced parts 1 and 1′ are located at location a and location brespectively of base shaft 5. When reinforced parts 1 and l′ areprovided at both location a and location b of the base shaft 5,improvement of ball flight direction may be expected together with amore convenient and exact swing.

[0081]FIG. 17 shows a golf club 29D made from a golf club shaft 25D inaccordance with a fourth embodiment of the invention in which a waveshaped reinforced part 1A is located at the midpoint m of base shaft 5.When reinforced part 1A is provided at midpoint m of base shaft 5,improvement of ball flight direction also may be expected together witha more convenient and exact swing.

[0082]FIG. 18 shows a golf club 29E made from a golf club shaft 25E inaccordance with a fifth embodiment of the invention in which a waveshaped reinforced part 1B is located between midpoint m and the loweredge of grip 27 of base shaft 5. When reinforced part 1B is provided atmidpoint m of base shaft 5, the kick point moves down and improvement ofball flight direction may be expected together with a more convenientand exact swing.

[0083] The golf club shaft of the present invention has variousadvantages such as: a) improvement of torsion characteristics of theshaft, b) controllable movement of the kick point of the golf club shaftto a desired location to improve the direction of a golf ball with amore convenient and accurate swing, and c) the ability to further extendthe length of the reinforced shaft to improve the flying distance of agolf ball without application of added force, i.e., without the need toemploy a higher swing speed. Another advantage is the ability to use ofcommercially available base shafts to produce the golf club shafts ofthe present invention thus avoiding the complicated manufacturingprocesses required by golf club shafts of the prior art.

[0084] Golf clubs made with the shafts of the present invention impartgreater flying distance and/or directional accuracy to golf balls struckby the golf clubs. The reinforced part provides a means of moving thekick point of the shaft to achieve a desired effect on flying distanceand/or accuracy. The present invention also provides a convenient meansof adjusting the characteristics of a golf club shaft according to theskill level of the intended user.

[0085] In addition, the wave-shaped reinforced part offsets the impactwave induced when impacting a ball, thus protecting the human body.

EXAMPLES

[0086] In an illustrative but non-limiting example, a commerciallyavailable carbon fiber prepreg sheet known as T700 obtained throughKorea Fiber Company of Korea and a commercially available glass fiberprepreg sheet are placed together and then the assembly is cut to form abase section with finger-like elements having curved edges as shown inFIG. 8. Base section 2B of the prepreg assembly is attached along thelength of the desired section of the base shaft by epoxy resin and thefinger-like elements are wrapped tightly around the base shaft to form awave shaped reinforced part that has a sinusoidal wave configuration.The resulting wave shaped reinforced part is covered with carbon tape.The covered wave shaped reinforced part is then heat cured by placingthe shaft having the wave shaped reinforced part into an oven at 80° C.and then raising the temperature to 120° C. over 30 minutes. Thereafter,the temperature is raised to 130° C. over 60 minutes. The shaft havingthe cured wave shaped reinforced part thereon then is removed from theoven and cooled to room temperature. After curing is completed, the tapeis removed by sandpaper, and the shaft is ground to remove anyimperfections and to give the resulting wave shaped reinforced part asmooth finish. Grinding may also be employed to alter the shape of areinforcement piece or pieces in the cured wave shaped reinforced partto achieve a desired wave configuration.

[0087] In another non-limiting example of the invention, a golf clubshaft such as that illustrated in FIG. 2 is produced. In this example,the golf club shaft includes a base shaft that has a weight of 62 gram,and total length of 1143 mm. The original kick point is located 46 cmfrom the club head tip of the shaft. In accordance with the invention,it is found that after adding a wave shaped reinforced part having alength of 20 cm and having 5 reinforcement pieces, the kick point movesdown to 44 cm from the club head tip of the shaft. The weight of theshaft having the reinforced part, measured prior to application offinishing materials such as lacquers and the like, is 68 grams. If it isdesired to the same height of kick point as the original base shaftprior to forming the reinforced part thereon, the length of the baseshaft may be extended by about 70 mm to about 110 mm.

[0088] The following Tables 2-4 show measurements of carry, and of carryand roll distances (in yards) for a golf club made from a commerciallyavailable golf club shaft (“CONTROL”) and the same type of golf clubmade from a golf club shaft according to the invention (“INVENTION”).The specifications of the Test Clubs were comparable. The clubs weretested in a mechanical swinging device wherein the club head speed was95 mph. CONTROL Test Club Head: Tour Edge Titanium 950-Driver (9.0°)Club Shaft: Aldila - R/S Flex INVENTION Test Club Head: Tour EdgeTitanium 950-Driver Club Shaft: Golf club shaft according to theinvention with the wave shaped reinforced part having five reinforcementpieces near the grip section. The upper edge of the reinforced part waslocated around 2.5 inches below a 10⅜ inch grip. The shaft was made froma graphite base shaft that was 45 inches long.

[0089] TABLE 2 Carry Carry and Roll CENTER HITS Distance (yds) AccuracyDistance (yds) Accuracy CONTROL 235.0 −0.8 281.8 −6.0 Std. Dev. 1.4 4.57.4 6.4 INVENTION 244.0 2.4 272.8 2.4 Std. Dev. 3.5 4.5 3.6 4.2

[0090] TABLE 3 Carry Carry and Roll ½ TOE HITS Distance (yds) AccuracyDistance (yds) Accuracy CONTROL 221.4 13.4 271.2 12.8 Std. Dev. 4.7 2.18.3 1.9 INVENTION 240.0 2.4 268.8 0.3 Std. Dev. 1.9 2.2 4.8 2.9

[0091] TABLE 4 Carry Carry and Roll ½ HEEL HITS Distance AccuracyDistance Accuracy CONTROL 215.4 −18.8 265.0 −20.0 Std. Dev. 4.6 3.7INVENTION 235.8 −27.6 271.0 −19.0 Std. Dev. 6.6 10.1 5.7 1.4

What is claimed is:
 1. A golf club shaft comprising a base shaft havingan internal surface and an external surface, and at least one waveshaped reinforced part on at least one of said surfaces, said waveshaped reinforced part comprising a plurality of reinforcement pieces.2. The golf club shaft of claim 1 wherein said golf club shaft includesan upper portion, a midpoint m, and a lower portion, said wave shapedreinforced part located on at least one of said upper portion, saidmidpoint m, and said lower portion.
 3. The golf club shaft of claim 2wherein said wave shaped reinforced part is located on said upperportion.
 4. The golf club shaft of claim 2 wherein said wave shapedreinforced part is located on said lower portion.
 5. The golf club shaftclaim 2 wherein said wave shaped reinforced part is located on saidmidpoint m.
 6. The golf club shaft of claim 1 wherein said plurality ofreinforcement pieces is at least three reinforcement pieces.
 7. The golfclub shaft of claim 6 wherein said wave shaped reinforced part is onsaid external surface of said base shaft.
 8. The golf club shaft ofclaim 7 wherein said wave shaped reinforced part has a length of about 2cm to about 20 cm.
 9. The golf club shaft of claim 8 wherein said waveshaped reinforced part has a sinusoidal configuration.
 10. The golf clubshaft of claim 1 wherein said reinforcement pieces comprise a carbonfiber prepreg sheet and a glass fiber prepreg sheet.
 11. A golf clubshaft having an external surface, comprising a base shaft having a tipend for receiving a club head and a grip end for receiving a grip, and awave shaped reinforced part on said external surface of said base shaft,wherein said wave shaped reinforced part has a length of about 20 cm andincludes at least 3 reinforcement pieces, said wave shaped reinforcedpart having a sinusoidal configuration, and wherein said reinforcementpieces comprise carbon fiber prepreg.
 12. The golf club shaft of claim11 wherein said waved shaped reinforced part has at least 5reinforcement pieces.
 13. The golf club shaft of claim 11 wherein saidreinforced part is located on said upper portion.
 14. The golf clubshaft of claim 11 wherein said base shaft has a length of about 1143 mmand a kickpoint located at about 44 cm from said tip end of said baseshaft.
 15. The golf club shaft of claim 11 wherein said reinforcementpieces further comprise glass fiber prepreg.
 16. A method of making agolf club shaft having a base shaft and a wave shaped reinforced partthereon comprising, applying a base section 2B of a prepreg sheet havinga plurality of finger like elements 2A to a portion of a base shaft,wrapping said finger like elements 2A around said base shaft to providea wave shaped reinforced part having a plurality of reinforcement pieceson said base shaft, and curing said shaft having said wave shapedreinforced part thereon to produce a golf club shaft having a waveshaped reinforced part thereon.
 17. The method of claim 16 wherein saidwave shaped reinforced part comprises at least 3 reinforced pieces. 18.The method of claim 16 wherein said base shaft has an upper portion, amidpoint m, and a lower portion, and wherein said wave shaped reinforcedpart is located on at least one of said upper portion, said midpoint m,and said lower portion.
 19. The method of claim 16 wherein said prepregsheet comprises a carbon fiber prepreg sheet.
 20. The method of claim 16wherein said prepreg sheet comprises a glass fiber prepreg sheet joinedto a carbon fiber prepreg sheet.
 21. A golf club comprising a golf clubshaft comprising a base shaft having an internal surface and an externalsurface, and at least one wave shaped reinforced part on at least one ofsaid surfaces, said wave shaped reinforced part comprising a pluralityof reinforcement pieces.
 22. The golf club of claim 21 wherein said golfclub shaft includes an upper portion, a midpoint m, and a lower portion,said wave shaped reinforced part located on at least one of said upperportion, said midpoint m, and said lower portion.
 23. The golf club ofclaim 22 wherein said wave shaped reinforced part is located on saidupper portion.
 24. The golf club of claim 22 wherein said wave shapedreinforced part is located on said lower portion.
 25. The golf clubclaim 22 wherein said wave shaped reinforced part is located on saidmidpoint m.
 26. The golf club of claim 21 wherein said plurality ofreinforcement pieces is at least three reinforcement pieces.
 27. Thegolf club of claim 26 wherein said wave shaped reinforced part is onsaid external surface of said tubular shaft member.
 28. The golf club ofclaim 22 wherein said wave shaped reinforced part has a length of about2 cm to about 15 cm.
 29. The golf club of claim 28 wherein said waveshaped reinforced part has a sinusoidal configuration.
 30. The golf clubof claim 21 wherein said reinforcement pieces comprise a carbon fiberprepreg sheet and a glass fiber prepreg sheet.